A variable displacement swash plate compressor used for a refrigeration circuit as shown in FIG. 11 has been proposed in the prior art. That is, a drive shaft 91 is rotatably supported by a housing 85, and a rotor 87 is fixed to the drive shaft 91 to be rotatable integrally with the drive shaft 91. A swash plate 92 is supported by the drive shaft 91 to be slidable in the direction of the axis L and tiltable with respect to the drive shaft 91. A hinge mechanism 88 is located between the rotor 87 and the swash plate 92. Single head pistons 94 are coupled to the outer circumferential portion of the swash plate 92 with semispherical first shoes 93A arranged toward the hinge mechanism 88 and semispherical second shoes 93B arranged opposite to the hinge mechanism 88. When the swash plate 92 is rotated by rotation of the drive shaft 91, the swash plate 92 slides with respect to the shoes 93A, 93B causing the pistons 94 to reciprocate, thereby compressing refrigerant gas.
The shoes 93A, 93B rotate about an axis S (a line that passes through the center of curvature P of semispherical sliding surfaces 93a and is perpendicular to sliding flat surfaces 93b with respect to the swash plate 92) as the shoes 93A, 93B rotate relative to the swash plate 92. The rotation of the shoes 93A, 93B about the axis S is caused because a rotational force is applied to the shoes 93A, 93B in one direction about the axis S due to the difference between the circumferential velocities of the inner and outer circumferences of the swash plate 92. More specifically, the circumferential velocity of the outer circumference of the swash plate 92 is greater than that of the inner circumference of the swash plate 92.
That is, the swash plate compressor shown in FIG. 11 is configured such that the shoes 93A, 93B directly slide against the swash plate 92. Therefore, the shoes 93A, 93B are unnecessarily rotated about the axis S due to the sliding motion caused as the shoes 93A, 93B rotate relative to the swash plate 92. This increases the mechanical loss particularly at the sliding portion between each piston 94 and the corresponding shoe 93B that receives reactive force of compression, and causes problems such as seizure at the sliding portions.
To solve these problems, it has been proposed to provide a roller bearing that receives a thrust load between the swash plate 92 and the shoes 93B [For example, Japanese Laid-Open Patent Publication No. 8-28447 (page 3, FIG. 1)]. In this case, as rolling elements of the roller bearing roll, the swash plate 92 slides with respect to the shoes 93B. This suppresses rotation motion of the shoes 93B about the axis S caused by relative rotation between the swash plate 92 and the shoes 93B. Therefore, the mechanical loss and occurrence of problems are suppressed.
However, when the swash plate 92 and the roller bearing are located in the limited space between the shoes 93A and the shoes 93B, the swash plate 92 is made thin and a predetermined strength may not be secured. Also, as for the piston 94 located in the vicinity of the top dead center position (in the compression stroke), a load from the shoe 93B that receives a significant reaction force of compression is concentrated on a particular rolling element of the roller bearing. Therefore, the durability of the rolling elements of such a small size that they can be arranged in the limited space between the shoes 93A and the shoes 93B (in other words, with low strength) may not be sufficient.
To solve such a problem, for example, a technique as shown in FIG. 12 has been proposed [for example, Japanese Laid-Open Patent Publication No. 8-338363 (page 4, FIG. 1)]. That is, an annular step 90a is provided at the center of a rear surface (a surface facing rightward in FIG. 12) of a first swash plate 90. An annular second swash plate 95 is arranged outward of the step 90a of the first swash plate 90. The second swash plate 95 is supported by the first swash plate 90 via a support hole 95a formed at the center of the second swash plate 95 to be rotatable relative to the first swash plate 90. The outer circumferential portion of the second swash plate 95 is arranged between the first swash plate 90 and the shoes 93B to be slidable with respect to the first swash plate 90 and the shoes 93B.
Therefore, when the first swash plate 90 is rotated, the first swash plate 90 slides relative to the second swash plate 95, which reduces the rotation speed of the second swash plate 95 as compared to the rotation speed of the first swash plate 90. This reduces the relative rotation speed of the second swash plate 95 and the shoes 93B (the relative rotation speed of the second swash plate 95 with respect to the shoes 93B) as compared to the relative rotation speed of the shoes 93B and the first swash plate 90 (the relative rotation speed of the first swash plate 90 with respect to the shoes 93B). As a result, the rotation of each shoe 93B about the axis S caused by the relative rotation of the second swash plate 95 and the shoes 93B is suppressed, which suppresses mechanical loss and occurrence of problems. Also, the second swash plate 95, which is a thin plate, is merely located between the shoes 93B and the first swash plate 90. This secures the thickness (or the strength) of the first swash plate 90, and a load from the shoe 93B of the piston 94 located in the vicinity of the top dead center position (in the compression stroke) that receives a significant reaction force of compression is dispersed and received by a large area of the second swash plate 95. Therefore, the durability of the second swash plate is sufficient.
However, when the first swash plate 90 is rotated, frictional resistance occurs between the inner circumferential surface of the support hole 95a of the second swash plate 95 and the first swash plate 90 (the step 90a) in addition to the outer circumferential portion of the second swash plate 95 located between the first swash plate 90 and the shoes 93B. This hinders the first swash plate 90 from sliding with respect to the second swash plate 95. Therefore, it is difficult to significantly reduce the relative rotation speed of the second swash plate 95 and the shoes 93B as compared to the relative rotation speed of the shoes 93A and the first swash plate 90. Therefore, the advantages (such as reduced mechanical loss) of providing the second swash plate 95 are not sufficiently obtained.
It has become a common practice to use carbon dioxide as refrigerant of the refrigeration circuit. When carbon dioxide refrigerant is used, the pressure in the refrigeration circuit becomes extremely high as compared to a case where chlorofluorocarbon refrigerant (for example, R134a) is used. Therefore, the reaction force of compression applied to the pistons 94 is increased in the swash plate compressor, which increases the pressure between the first swash plate 90 and the second swash plate 95, and the aforementioned problem has become a significant matter of concern.
Patent Document 1: Japanese Laid-Open Patent Publication No. 8-28447 (page 3, FIG. 1)
Patent Document 2: Japanese Laid-Open Patent Publication No. 8-338363 (page 4, FIG. 1)